The ability to cool a laser diode has been widely recognized as a limitation of current day ability to convert electrical energy into coherent radiant energy in a small space. Since present day laser diodes operate in the realm of fifty percent or lower electrical energy to light energy conversion efficiency and laser diode operation in the temperature range around room temperature are usual factors incurred in laser operation, it is easy to comprehend that efficient removal of unconverted electrical energy proceeds or energy losses, i.e., heat, from a for example, laser bar structure is highly desirable.
One of the better heat removal arrangements currently known in the laser diode art originates in commendable work accomplished by a team of specialists working in the Lawrence Livermore National Laboratory (Lawrence), a United States Government owned laboratory operated for the Government of the U.S. by the University of California. The Lawrence cooling arrangement involves a Silicon Monolithic Microchannel (SiMM) apparatus in which a liquid such as water flowing in an array of closed cross section sub surface channels accomplishes the ultimate removal of heat from a laser diode array. Several U.S. patents describe the Lawrence cooling arrangement; these patents include U.S. Pat. No. 5,828,683. Several other U.S. patents relating to such cooling, patents by Lawrence colleagues and others, are identified in the list of references submitted with the present patent application. Each of these patents, the other patents identified in connection with the present application and the publication references identified in connection with the present application are hereby incorporated by reference herein.
A brief consideration of characteristics of the best available laser diode Silicon Monolithic Microchannel cooling arrangement illustrates the existence of need in the art for even more improved laser diode thermal management tools. To this end the thermal resistance of the Lawrence Silicon Monolithic Microchannel apparatus is estimated to be approximately 0.05 degree Celsius/Watt for a 1 cm2 area due to the thermal conductivity of the employed silicon and the thickness of the carrier structure. For a hypothetical thermal load of 1000 Watts/cm2 that may occur during high power operation of a laser bar, this means the temperature of the top laser mounting surface of the Silicon Monolithic Microchannel will be about 50 degrees Celsius higher than the temperature of the cooling or bottom surface of the Silicon Monolithic Microchannel. Hence it may be appreciated that the efficiency of the Silicon Monolithic Microchannel cooling system is reduced by thermal resistance. In the case of the present invention Integrated Diamond Carrier, the difference between the top laser mounting surface and that of the cooling or bottom surface is only 1 degrees Celsius however as is explained below.
The Silicon Monolithic Microchannel incorporates a cooling system built into the carrier itself, however it incurs difficulties relating to temperature variations from the cooling liquid flow directionality, and with conditions relating to high heat loads. In the latter instance the pressure of the cooling liquid necessary to cool effectively is often excessively high and can damage the built in Silicon Monolithic Microchannel cooling channels. In addition, the Silicon Monolithic Microchannel built in cooling channels are complex and expensive to fabricate.
Other more traditional laser diode packages include arrangements wherein laser bars or other sources of heat loss are clamped between copper plates and mounted on a common carrier. In these arrangements, heat is removed from the laser through the copper plates by the cooling system. The overall thermal resistances achieved with these types of packages are however usually even higher than that incurred with the Silicon Monolithic Microchannel.
Additionally fabrication of a Silicon Monolithic Microchannel device and the more traditional laser bar packages are notably more complex than the simple planar fabrication process of the present invention IDC; especially when the manner in which conventional devices direct the laser beams is considered. Notably the arrangement of the present invention IDC is also well suited for use with highly efficient liquid spray cooling techniques.
As may be appreciated by even a cursory review of the publication references identified in connection with the present application it has for years been suggested that laser diode heat sinks or heat transfer elements made from diamond material can be of assistance in the removal of heat energy losses from a laser diode, a solid state laser. Indeed a number of diamond-inclusive thermal energy management arrangements for such diodes have been disclosed over a period of some thirty or so years. The present invention provides an especially advantageous improvement in this area.